1. Field of the Invention
This invention relates to a tone arm driving apparatus, and more particularly to an electromagnetic tone arm driving apparatus for a phonographic record player.
2. Description of the Prior Art
In a conventional tone arm driving apparatus for a fully automatic record player, rotational energy from the turn table or a special, separate electric motor is used as a drive source for driving the tone arm. The tone arm is driven by the drive source through mechanical transmitting means such as gears, cams, and links. The record player is so designed as to perform various operations such as "lead-in operation," "reject operation," "auto-return operation," "arm-up operation" and "arm-down operation" by driving the tone arm.
Since the tone arm is driven through a mechanical construction, the tone arm driving apparatus has a slow or retarded response due to the cams and gears. Many times an operating button must be depressed for a considerably long period of time to perform a necessary operation. Further, the tone arm driving apparatus is complicated in construction, troublesome to assemble, and the amount of labor required for adjustment is large. Finally, it is relatively expensive.
In consideration of the above described problems, attempts to electromagnetically drive a tone arm have been made. For example, in the German Auslegeschrift No. 1,917,241, a bobbin, to which a pair of sectorial coils are attached, is fixed to a horizontal drive shaft for a tone arm, and a permanent magnet is arranged facing the coils. When one of the coils is energized, a horizontal drive force is obtained to horizontally rotate the tone arm. At this time, the horizontal rotational speed of the tone arm is detected by the other coil.
A leaf spring is provided for controlling the vertical rotation of the tone arm. A wire is connected to the top end of the leaf spring so as to elastically bias the leaf spring downwardly. When a current is supplied to the wire, the latter generates heat and expands. The leaf spring is elastically restored with the expansion of the wire. The tone arm is moved upwardly with the restoration of the leaf spring. Thus, the vertical drive of the tone arm is not performed in electro-magnetic manner. Additionally, the number of parts is large, the apparatus is retarded in response, and further, it does not have a long useful life.